From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yuchung Cheng Subject: Re: [PATCH RFC net-next 0/2] tcp: Redundant Data Bundling (RDB) Date: Fri, 23 Oct 2015 23:11:00 -0700 Message-ID: References: <1445633413-3532-1-git-send-email-bro.devel+kernel@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <1445633413-3532-1-git-send-email-bro.devel+kernel@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: =?UTF-8?Q?Bendik_R=C3=B8nning_Opstad?= Cc: "David S. Miller" , Alexey Kuznetsov , James Morris , Hideaki YOSHIFUJI , Patrick McHardy , Jonathan Corbet , Eric Dumazet , Neal Cardwell , Tom Herbert , Paolo Abeni , Erik Kline , Hannes Frederic Sowa , Al Viro , Jiri Pirko , Alexander Duyck , Florian Westphal , Daniel Lee , Marcelo Ricardo Leitner , Daniel Borkmann , Willem de Bruijn , =?UTF-8?Q?Linus_L=C3=BCssing?= , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-api@vger.kernel.org On Fri, Oct 23, 2015 at 1:50 PM, Bendik R=C3=B8nning Opstad wrote: > > This is a request for comments. > > Redundant Data Bundling (RDB) is a mechanism for TCP aimed at reducin= g > the latency for applications sending time-dependent data. > Latency-sensitive applications or services, such as online games and > remote desktop, produce traffic with thin-stream characteristics, > characterized by small packets and a relatively high ITT. By bundling > already sent data in packets with new data, RDB alleviates head-of-li= ne > blocking by reducing the need to retransmit data segments when packet= s > are lost. RDB is a continuation on the work on latency improvements f= or > TCP in Linux, previously resulting in two thin-stream mechanisms in t= he > Linux kernel > (https://github.com/torvalds/linux/blob/master/Documentation/networki= ng/tcp-thin.txt). > > The RDB implementation has been thoroughly tested, and shows > significant latency reductions when packet loss occurs[1]. The tests > show that, by imposing restrictions on the bundling rate, it can be m= ade > not to negatively affect competing traffic in an unfair manner. > > Note: Current patch set depends on a recently submitted patch for > tcp_skb_cb (tcp: refactor struct tcp_skb_cb: http://patchwork.ozlabs.= org/patch/510674) > > These patches have been tested with as set of packetdrill scripts loc= ated at > https://github.com/bendikro/packetdrill/tree/master/gtests/net/packet= drill/tests/linux/rdb > (The tests require patching packetdrill with a new socket option: > https://github.com/bendikro/packetdrill/commit/9916b6c53e33dd04329d29= b7d8baf703b2c2ac1b) > > Detailed info about the RDB mechanism can be found at > http://mlab.no/blog/2015/10/redundant-data-bundling-in-tcp, as well a= s in the paper What's the difference between RDB and TCP repacketization (http://flylib.com/books/en/3.223.1.226/1/) ? Reading the blog page, I am concerned the amount of change (esp on fast path) just to bundle new writes during timeout & retransmit, for a specific type of application? why not just send X packets with total bytes < MSS on timeout.. > "Latency and Fairness Trade-Off for Thin Streams using Redundant Data > Bundling in TCP"[2]. > > [1] http://home.ifi.uio.no/paalh/students/BendikOpstad.pdf > [2] http://home.ifi.uio.no/bendiko/rdb_fairness_tradeoff.pdf > > > Bendik R=C3=B8nning Opstad (2): > tcp: Add DPIFL thin stream detection mechanism > tcp: Add Redundant Data Bundling (RDB) > > Documentation/networking/ip-sysctl.txt | 23 +++ > include/linux/skbuff.h | 1 + > include/linux/tcp.h | 9 +- > include/net/tcp.h | 34 ++++ > include/uapi/linux/tcp.h | 1 + > net/core/skbuff.c | 3 +- > net/ipv4/Makefile | 3 +- > net/ipv4/sysctl_net_ipv4.c | 35 ++++ > net/ipv4/tcp.c | 19 ++- > net/ipv4/tcp_input.c | 3 + > net/ipv4/tcp_output.c | 11 +- > net/ipv4/tcp_rdb.c | 281 +++++++++++++++++++++++= ++++++++++ > 12 files changed, 415 insertions(+), 8 deletions(-) > create mode 100644 net/ipv4/tcp_rdb.c > > -- > 1.9.1 >